UN talks ending Thursday failed to hammer out a draft of the "operating manual" that would bring the landmark Paris climate treaty to life, forcing governments to add an emergency negotiating session ahead of a December climate summit.
"We have been here for two weeks and fell short of what was foreseen," Elina Bardram, the European Union's top climate negotiator, told AFP.
"We were not even close."
The 197-nation Paris Agreement, inked in 2015, calls for capping global warming at "well under" two degrees Celsius (3.6 degrees Fahrenheit), and 1.5 C if feasible.
The global thermometer has risen by one degree since the mid 19th-century, enough to see a crescendo of climate-enhanced droughts, floods, heat waves and superstorms.
Voluntary national pledges to reduce carbon pollution would still allow temperatures to rise by three degrees or more, unleashing forces that could pull at the fabric of civilisation, say scientists.
The agreement also promises at least $100 billion (85 billion euros) per year from 2020 to help poor countries wean their economies from fossil fuels and cope with climate impacts, present and future.
But the devil is in the details, almost all of which remain to be ironed out.
How will national pledges to slash greenhouse gas emissions be measured and verified? By whom? Should China, India and other emerging economies be held to the same standards as Europe, Japan and the United States?
On money, where are the billions promised going to come from? Will they be loans or grants, from governments or banks?
These and hundreds of other questions need to be sorted by the end of the December 3-14 UN climate summit in Katowice, Poland. The Paris Agreement enters into force in 2020.
But during the 11-day talks in Bonn "the pace of work was too slow," said Amjad Abdulla, chief climate negotiator for The Maldives and spokesman for dozens of small island states threatened by rising seas.
The highly technical talks have roiled a decades-old schism between rich and developing nations that could hamper completion of what negotiators call the Paris "rule book".
Developing nations led by China and India, for example, have said reporting requirements for the so-called "nationally determined contributions" of wealthy countries should be more stringent, and detail the level and timing of financial aid to climate-vulnerable nations.
For developed nations, this is uncomfortably reminiscent of the two-tiered system -- a few dozen rich countries in one column, the rest of the world in another -- underlying the ill-fated Kyoto Protocol.
"The European Union acknowledges that there are differences in capabilities," said Bardram. "What we don't accept is that there would be a strict bifurcation between developed and developing countries."
Disagreements over money remain the biggest roadblock to progress.
"The finance issue has been so polarised and political, that there has not been any give on this so far," said Alden Meyer, director of strategy and policy for the Union of Concerned Scientists, a Washington-based advocacy and research group.
US President Donald Trump's decision to pull out of Paris pact, and his administration's efforts to boost fossil fuel technologies, have not helped.
"Trump is doing tremendous damage on the climate finance front," said Meyer.
"There is no one putting forward the $2 billion (1.68 billion euros) to replace the Green Climate Fund pledge that Trump is not going to honour."
For developing countries, this stalemate has undermined the still fragile foundation on which the Paris pact was built.
"The radio silence on money has sown fears among poor countries that their wealthier counterparts are not serious about honouring their promises," said Mohamed Adow, lead climate expert for Christian Aid.
A parallel track at the talks have sought to lay the groundwork for a new round of carbon cutting pledges to help close the so-called "emissions gap".
The Paris Agreement calls for revisiting current committment in 2023, but on current trends, experts warn, that may be too late.
Many key issues will be taken up at half-a-dozen ministerial and summit meetings between now and December.
"That's something the negotiators can't work out," said Meyer.
The added negotiation session will take place in Bangkok from September 3 to 8.